1. Field of the Invention
The present invention relates to a wavelength converter which receives signal light having a first wavelength and generates and outputs signal light having a second wavelength and carrying the same information as the received signal light.
2. Description of the Related Art
A wavelength converter receives signal light having a first wavelength and generates and outputs signal light having a second wavelength and carrying the same information as the signal light having the first wavelength. A wavelength converter is, for example, disposed at a node of an optical transmission network where a plurality of nodes are connected to each other by a network of optical fiber transmission lines, and converts a wavelength of input signal light that has reached the node and output the signal light whose wavelength has been converted as output signal light.
For example, a wavelength converter, disclosed in Japanese Patent Application Publication No. 2001-42368, comprises a semiconductor optical amplifier and a resonator. In the wavelength converter, a part of spontaneous emission from the semiconductor optical amplifier resonates in the resonator and acts as optical pump light, while input signal light is introduced into the resonator from the outside. The optical pump light and the input signal light interact with each other in the semiconductor optical amplifier, which is a wavelength converting medium, to generate output signal light, which is output from the resonator.
However, the wavelength converter, which makes use of spontaneous emission from the semiconductor optical amplifier such that the wavelength region of the emitted spontaneous emission and the wavelength region of the output signal light overlap, is inferior in terms of signal-to-noise (S/N) ratio of the output signal light. In addition, it has a disadvantage in that the available wavelength region of the output signal light cannot be wide since the usable wavelength region is determined in accordance with the gain characteristic of the semiconductor optical amplifier.